An ophthalmic lens blank generally has a first face with a pre-determined curvature and a second face, opposite the first face on which a desired surface contour is generated by a machining process. The overall process is generally referred to as “lens surfacing” and the overall object is to yield a finished spectacle lens L (shown in section in. FIG. 4) so that the curvature of the first (in this instance convex) face cx and the curvature of the machined second (in this instance concave) face cc cooperate to yield desired optical properties according to the prescription. In addition to this the first and/or second faces cx, cc of the lens L are usually coated (cf. FIG. 5 illustrating in an enlarged view of detail V in FIG. 4 an example for such coating) to provide the finished spectacle lens L with an enhanced ability to resist scratching (by use of a “hard coating” HC), with a low residual reflection and a desired color (by use of an “antireflection coating” AR), and/or with certain surface properties such as hydrophobic, oleophobic and dust repelling properties (by use of a “top coating” TC). Usually also a further machining process takes place (the so-called “edging”), the aim of which is to finish-machine the edge E of the spectacle lens L in such a way that the spectacle lens L may be inserted into a spectacle frame. In all these process steps the spectacle lens (blank) L must reliably be held in any machining machine and coating apparatus respectively.
To this end the prior U.S. patent application Ser. No. 12/919,328 discloses a special block piece for holding the spectacle lens (blank) throughout the above mentioned processing steps. To be more precise, prior to the processing the lens blank with its first face cx is “blocked” with the aid of a blocking material—for instance a UV or visible light (VIS) radiation curable adhesive composition—on a workpiece mounting face portion of this block piece, where it remains throughout the processing until the processed spectacle lens L is “deblocked” again from the block piece. So as to further minimize the production efforts in the prescription workshop it has further been proposed in the U.S. patent application Ser. No. 12/919,328 to fully finish the first, blocking face cx of the lens blank prior to the blocking step, including hard coating HC, antireflection coating AR and, if required, top coating TC.
The hydrophobic and/or oil-repellent anti-stain top coatings TC however most often are made from fluorosilane-type materials that reduce the surface energy so as to prevent the adhesion of greasy stains which are thereby easier to remove. One of the problems associated with such top coating TC is that it may achieve such an efficiency that the adhesion at the interface between the blocking material and the first, blocking face cx of the lens blank is thereby altered. As a result there is a risk that the adhesive connection between the lens blank and the block piece cannot sufficiently withstand the forces that are exerted on the lens blank during the machining thereof. At the worst, the lens blank comes off the block piece and is ruined.
In order to address such problem it has been proposed already (cf. US-A-2003 0049370) to coat onto a lens blank comprising an outer hydrophobic and/or oil-repellent surface coating, a temporary protective layer imparting to the lens blank a surface energy at least equal to 15 mJ/m2 so as to achieve a sufficient adhesion at the interface between a holding pad and the lens blank for holding pads conventionally used in the technical field to hold the lens blank on a block piece during the machining steps.
However with this approach it is difficult already to provide for sufficient adhesion at the interface between the hydrophobic and/or oil-repellent surface coating on the one side and the temporary protective layer on the other side. Once sufficient adhesion has been achieved at this interface it must be ensured that the hydrophobic and/or oil-repellent surface coating is not damaged upon removal of the temporary protective layer after processing the lens. This is exceptionally difficult if both the hydrophobic and/or oil-repellent surface coating and the temporary protective layer consist of an organic material.
What is needed is a method for manufacturing spectacle lenses according to a prescription, that overcomes the drawbacks previously cited and enables in particular spectacle lenses with high optical qualities to be produced more quickly and at lower cost, without the risk that the spectacle lens blank unintentionally comes off the block piece during the processing steps.